Friction contact damper



5, 1951 F. B. WOESTEMEYER' 2,540,854

FRICTION CONTACT DAMPER Filed March 29, 1949 Inventor": Francis B.Woestemeyer,

bym His Attorney.

Patented Feb. 6, 1951 FRICTION CONTACT DAMPER Francis B. Woestemeyer,Schenectady, N. Y., assignor to General Electric Company, a corporationof New York Application March 29, 1949, Serial No. 84,203

7 Claims. (Cl. 200-166) My invention relates generally to devices forthe elimination of contact rebound in electrical contactors.

When an electrical switch or relay closes, as a result of force beingexerted ona contact-carrying member, there is normally a tendency forthe contacts to rebound and fly apart momentarily. This causes arcing atthe contacts which may produce a weld at the contact points, causingthem to stick. This phenomenon is commonly known as rebound freezing ofthe contacts and is a major source of failures of such units.

My invention is more particularly concerned with an electrical switchcomprising a contactor carried on a rotating member or wheel. A numberof contactors are fixed in position about the are described by therotating contactor in a manner to interrupt 'its path. Such a switch,along with its manner of operation, is described in my copending UnitedStates patent application No. 84,202, dated March 29, 1949, and entitledCommutator Timing Mechanism, which application is assigned to the sameassignee as the present invention. It has been found that when therotating contactor strikes one of the fixed contactors, there is amomentary rebound which may cause arcing at the contacts with resultinguncertainty of operation.

Accordingly, it is an object of my invention to provide a new andimproved device for reducing the rebound of a rotating contact so as toprevent freezing thereof.

Another object of my invention is to provide a device for exerting anincreased pressure on a rotating contact after it strikes a fixedcontact, thereby eliminating the possibility of contact rebound and aresulting momentary open circuit.

In accordance with my invention, I provide a friction disc which iscoupled to a wheel carrying a rotating contact. When the rotatingcontact strikes a fixed contact, the friction disc continues itsrotation for a short time interval; and through its coupling with theinertia wheel it increases the pressureat the contacts, therebycounteracting the tendency to rebound. The energy which would otherwisehave gone into the rebound is thus dissipated in braking the frictiondisc.

For further objects and advantages and for a better understanding of theinvention, attention is now directed to the following description andaccompanying drawing, and also to the appended claims in which thefeatures of the invention believed to be novel are more particularlypointed out.

In the drawings,

Fig. 1 is a pictorial illustration of a rotating contact mechanismembodying my invention.

Fig. 2 is a sectional view of part of the mechanism of Fig. 1 with whichmy invention is more particularly concerned, comprising an inertia wheeland a magnetically retained friction disc.

Fig. 3 is a front elevation view of the friction disc shown in Figs. 1and 2 and illustrating its magnetic characteristics.

Fig. 4 is a sectional view of another embodiment of my inventioncomprising a spring retained friction disc, which is adapted to operatein conjunction with the mechanism shown in Fig. 1.

Referring to Fig. 1., there is shown an inertia wheel I having anelongated hub 2 which is mounted to rotate freely on a shaft 3. A spiralspring 4' is fixed at one end to hub 2 and at the other end to a drivingwheel 5 which is adapted a contactor 6. A number of fixed contacts, of

which three are shown in the drawing, namely, 1, 8 and 9, are disposedabout the periphery of the inertia wheel in a manner to intercept thecontactor 6 when the wheel rotates. The heads of the fixed contacts haveconical points and these intercept a bent portion of the rotatingcontactor. A member ID normally restrains the inertia wheel and the hubfrom sliding longitudinally along shaft 3.

When it is desired that the rotating contactor advance from one fixedcontact to the next, member I0 is moved to the left. This permits theinertia wheel and the hub to slide along the shaft to the left by anamount sufficient to enable the bent portion of the rotating contactorto disengage itself from fixed contact I. The spiral spring thenaccelerates the inertia wheel and member l0 returns the wheel to itsprevious longitudinal position on shaft 3 so that the rotating contactoris intercepted by the fixed C011? tact 8 upon reaching its angularposition.

The apparatus as described so far would suffer from excessive reboundwhen the rotating contactor strikes the fixed contacts. In accordancewith my invention, this is prevented by a magnetized steel disc I2 whichis mounted about hub 2 in proximity to the inertia wheel. The holethrough the center of the disc is of a greater diameter than that of hub2 so that the disc is not restrained by the hub from rotating.

- Referring to Figs. 2 and 3, the disc is bent into an open 0 shape andmagnetized along a diame- 3 ter which coincides with the plane ofmaximum bending. This insures that the poles of the magnetic field inthe disc coincide with the points of contact of the disc with theinertia wheel,

thereby assuring maximum contact friction. In

practice, the magnetized disc is made of a permanently magnetizablealloy and the inertia wheel is made of mildsteel. This combinationprovides a permanent magnetism in the disc and a low residual magnetismin the inertia wheel. Thus, there is always maximum attraction betweenthe disc and the wheel, and there is no possibility of a permanentmagnetism being established in the inertia wheel so as to lock the discin one fixed position with respect to the inertia wheel.

In operation, the magnetic attraction of the disc and wheel causessufiicient friction at the contact points so that the disc acceleratesat the same rate as the wheel when it begins to rotate. When therotating contactor 6 strikes a fixed contact, such as contact I, thewheel stops very suddenly and has a tendency to rebound and reverse itsdirection of rotation. However, the coupling between the disc and wheelis insuflicient to stop the discs rotation as quickly, and it continuesto rotate for a short interval of time, meanwhile exerting a torque onthe wheel. This additional torque is sufiicient to substantiallyeliminate the rebound of the contacts, thereby preventing arcing througha momentary open circuit. The torque exerted on the wheel by the disc islargely the result of friction at the contact faces, although some of itis due to induced currents caused by magnetic interlinking.

In an actual construction of a rotating contact mechanism, similar tothat illustrated in Fig. 1 it was found that without the friction discthe rebound interval of the contacts was 0.010 second. In other words,immediately after striking a fixed contact, the rotating contactor wouldrebound, and an open circuit would occur which would last for the abovementioned time interval. With the addition of a friction disc asdescribed, the contact rebound interval was reduced to a maximum of0.001 second with no rebound apparent most of the time.

Referring to Fig. .4, there is shown another embodiment of my inventioncomprising the inertia wheel I, of which the hub 2 has been modifled bythe addition of a shoulder 83. The magnetic friction disc I2 isreplacedby a fiat unmagnetized friction disc M, and a spiral spring I5abutting on the shoulder l3 presses the disc against the inertia wheel.In this embodiment, the spiral spring creates the pressure between thefriction disc and the inertia wheel, and the friction damping occurs ina similar fashion to that in the embodiment illustrated in Fig. 2.

While certain specific embodiments have been shown and described, itwill, of course, be understood that various modifications may be tionalinertia, said inertia, upon engagement of said contactors being ofsufiicient value to overcome said coupling to permit rotation of saidfriction member relative to said rotating member,

2. A friction contactor adapted to eliminate rebound of a movingcontactor carried b a 1- tating member upon engagement with anothercontactor, comprising a friction disc pivoting with said member, meansfor providing friction coupling between said disc and said memberwhereby said disc acquires arotational inertia,

said inertia, upon engagement of said contactors being of sufficientvalue to overcome said coupling to permit rotation of said frictionmember relative to said rotating member.

3. A friction contact damper adapted to eliminate rebound of a contactorcarried'by a rotating member upon striking a fixed contactor comprisingmeans for exerting a positive pressure on said rotating contactor in.the direction oi its travel after striking said fixed contactor, saidmeans comprising a permanently magnetized friction disc pivotablymounted on said member,

said rotating member being made of magnetizable material to provide africtional coupling with said friction disc due to magnetic attractiontherebetween, said friction disc having a given rotational inertia insaid direction of travel to overcome said frictional coupling uponstriking of said contactors to continue rotating in said having a givenrotational inertia in said direction of travel to overcome saidfrictional coupling upon striking of said contactors to continuerotating in said direction of travel.

5. An electrical switch comprising a contactor carried by a rotatingwheel, a fixed contact located around the are described by saidcontactor, in a manner to engage said contactor, a friction disc mountedcoaxially with said wheel and in close proximity thereto, said wheel anddisc being made, one of permanently magnetized material, and the otherof a magnetizable material whereby said disc is maintained in contactwith said wheel due to magnetic attraction to develop a rotationalinertia, said inertia upon engagement of said contactor and contactbeing of sufficient value to overcome said attraction to permit rotationof said disc relative to said wheel.

6. An arrangement for eliminating rebound of a moving contactor carriedby a rotating member upon striking another contactor comprising afriction member, friction coupling means for rotationally driving saidfriction member with said rotating member without slipping whereby saidfriction member acquires a given rotational inertia in the direction ofits travel, said inertia, upon said contactors striking one anotherbeing suflicient to reduce the degree of said frictional contact tocause slipping and said friction member continues to rotate in saiddirection of travel relative to said rotating member.

7. In combination, a moving cont/actor carried by a moving member forengaging another con tactor, a friction member, means for coupling saidmembers whereby said friction member acquires an inertia, said inertia,upon engagement oi! said contactors being 01' suiiicient value toovercome said coupling to a degree permitting movement of said frictionmember relative to said moving member.

FRANCIS B. WOESTEMEYER.

REFERENCES CITED The following references are of record in the file ofthis patent:

Number 6 UNITED STATES PATENTS Name Date Bijur Apr. 17, 1917 Hall Apr.13, 1920 Kintzing Mar. 30, 1928

